Circularly polarized microwave coupler



Nov. 5, 1957 P. J. SFERRAZZA CIRCULARLY POLARIZED MICROWAVE COUPLER Filed March 16, 1955 INVENTOR PETER (1.5FE

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. ATTORNEY United States PatentO CIRCULARLY POLARIZED MICROWAVE COUPLER Peter J. 'Sferrazza, Wantagh, N. Y., assignor to Sperry Rand Corporation, a corporation of Delaware Application March 16, 1955, Serial No. 494,193

:2 Claims. 01. 333- This invention relates to ultra high frequency apparatus, and more particularly, is concerned with a circular polarization type wave guide junction.

It has heretofore been proposed to measure impedance or standing-waves in a hollow wave guide transmission system by means of a circular wave guide which is coupled to the rectangular wave guide transmission line in a manner to produce circularly or elliptically polarized energy in the circular wave guide, the direction of rotation of the circularly polarized wave being determined by .waves in the circular wave guide from the energy transmitted in the rectangular wave guide transmission line.

It is the general object of this invention to providean improved circular polarization coupler suitable for use in impedance measuring apparatus of the type above described. Y

Another object of this invention is the provision of a circular polarization coupler in which the circularity of the coupled wave in'the circular wave guide portion of the coupler is unaffected by changes infrequency over a very broad frequency band of the energy transmitted in the rectangular wave guide transmission line in which the coupler is connected. i

' These and other objects of the invention which will become apparent as the description proceeds are achieved by the provision of a wave guide transition for coupling from a rectangular wave guide operatingin the TE10 mode to a circular wave guide operating in the circularly polarized TEii mode. The rectangular wave guide is directionally coupled to the respective narrow and broad walls of two adjacent intermediate rectangular wave guides, the intermediate wave guides in turn being directionally coupled to the circular wave guide at regions displaced circumferentially by ninety degrees to obtain the desired space quadrature relationship betweenthe two components of the circularly polarized wave. A pair of .ninety degree phase shifters areinserted in one of the inpreferred embodiment of the invention;

Fig. 2 is a sectional view taken on line 2--2 of Fig. 1;

2,812,497 Patented Nov. 5, 1957 ice In the figures, the numeral 10 indicates generally a-sec tion of a rectangular wave guide which may be part of a transmission line between a source 12 of microwave energy and a load 14. The rectangular wave guide section 10 serves to transmit energy in the TE10 mode. Extending parallel to the rectangular wave guide section are first and second intermediate rectangular wave guide sections 16 and 18. A narrow wall of the intermediate wave guide section 16 is common with a broad wall of the wave guide section 10, while a broad wall of the intermediate wave guide section 18 is common with the narrow wall of the wave guide section 10, as best seen in Fig. 2. V i

Suitable directional coupling means, such as a plurality of apertures 22, are provided in the common wall between wave guide sections 10 and 16 for providing coupling inthe forward direction therebetween. The amount of coupling is relatively small, there being preferably of the order of 19 db attenuation in the coupled energy. Similarly, suitable directional coupling means, such as a plurality of apertures 24, are provided in the common wall between the wave guide sections 10 and 18 for coupling energy in the forward direction therebetween.

Positioned in tangential relationship to a broad wall of wave guide section 16 and to a narrow wall of the wave guide section 18, in the manner best shown in Fig. 2, is a section of circular wave guide 26. Suitable directional coupling means, such as a plurality of apertures 28,:between the broad wall of the wave guide section 16 and the wall of the circular wave guide 26, couples energy in the forward direction between the wave guide section 16 and the circular wave guide section 26. Similarly, suitable directional coupling means, such as a plurality of apertures 30, in the common wall formed between the wave guide section 18 and circular wave guide section 26, provides forward'coupling therebetween. Because of the tangential relationship between the circular wave guide section 26 and the rectangular wave guide sections 16 and 18, it will be evident that the directional coupling means provided by the apertures 28 and 30 respectively couple waves in the TEn mode in the circular wave guide having polarization planes substantially at right angles to each other. Y

The apertures 28 and 30 are preferably positioned close to the corners of the respective wave guides 16 and 18 so that the amount of coupling in the two directional couplers so formed are substantially equal. are designed in number, size, and spacing to effect substantially power transfer. The directional coupling design involved to obtain the desired results is commonly known in the art. See, for example, Patent No.

Positioned between the directional coupling means provided by the apertures 22 and the directional coupling means provided by the apertures 28 in the wave guide 16 is a ninety degree phase shifter, indicated at 32.. The phase shifter as shown is preferably of the type described in the article A Wide Band Wave Guide Phase Shifter by G. J. Alfred, Proceedings of I. E. E., volume 100, part 3, No. 65, May 1953, pages 117-124. The phase shifter comprises a stepped dielectric block in which the steps are dimensioned according to the theory set forth in the mentioned article. Such a phase shifter is characterized by the fact that the phase shift is substantially unaffected by changes in frequency over an extremely wide frequency band. Asa result of the phase shifter 32, en-

ergy from the source 12 coupled to the circular waveguide through the intermediate wave guide 16 is in phase quadrature with respect to the energy coupled to the circular wave guide through the intermediate wave guide section a-p sp t iwgfth smb d maata Fig.

18. Thus, it will be seen that the incident energy in the wave guide 10 from the source 12 produces two wave components in thecircular wave guide 26 which are in The apertures space and phase quadraturew-The resultant of these two wave components in the circular wave guide 26 is a circularly polarized wave having a clockwise direction of rotation as viewed looking in the direction of propagation, according-to the arrangement above described and illustrated in the figures. v

Although the directional coupling means "provided. by theapertures28 and 30 is preferably designed to produce substantially a 100% power coupling between the intermediate wave, guides 16 and 18 and the circular wave guide "26, energy absorbing material indicated at 34 is positioned in the adjacent ends of the intermediate wave guide sections 16 and 18 to absorb any energy not coupled to' the circular wave guide 26, thus suppressing reflections and resultant standinggwaves in the intermediate waveguide sections '16 and 18. The opposite ends'of the intermediate wave guide sections 16 and 18 are terminated in short circuits, as provided, by conductive endplates indicated at 36 and '37., Thus, energy coupledqinto the intermediate wave guides Hand 18 from energy reflected down the wave 'guide from the load ,14 is reflected by the end plates 36and"37;back along the waveguide sections 16 and 18 and is coupled by-the apertures 28 and 30 into the circular wave guide section26 to form two plane polarized H waves in space quadrature. p

b A second phase shifter 38 is positioned in the intermediate wave guide section 16 between the directional coupling meansprovided by the apertures 22 and the reflecting end'plate 36. The phase shifter 38 is designed to produce ninety degrees phase shift in the same manner as the phase shifter 32. Thus the reflected energy from the load 14 coupled to the circular wave guide 26 through (the intermediate wave guide section 16 is shiftedby 270 degrees relative to, the reflected energy that i s coupled to the circular wave guide 26 through, the intermediate wave guide section 18. The additional 180 degrees phase shift'introduced by the phase shifter 38 from energy sampled from the reflected wave in the wave guide section 10. produces:circ.ularly polarized energy in,the circular wave guide 26 having the opposite direction of rotation, namely,- a counterclockwise direction of rotation as viewed in'the direction of.propagation. a

From the above description it will be seen that various objects ofthe invention have been achieved by thefprovision of apparatus that samples the energy in a rectangular wave guide transmission line, producing circularly polarized waves. in response thereto having a direction 'of rotation determined by the direction of propagation of the sampled energy in the transmission, line, ,ineident energy'frorn the source12 producing circularly polarized energy having one direction of rotation and reflected energy from the load 14 producing circularly polarized energy of the opposite direction of rotation:

With the exception of the phase shifters 32 and 38,

,the apparatus iselectrically symmetrical, soith at the cir- ,cularity of the circular polarized wave inthe wave guide -26 is unaffected ,by frequency. Thepath lengths provided-by the two intermediatewave guide sections are physically equal and the directional couplers are designed tobe physically, identical. Thus any etfectdue to,fre-

quency in the one path is duplicated in the other path. By designing the phase shifters, 32 and38 to intr oduce the correct phase shift over a large frequency band, which matter contained inthe above description or "shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Ultra-high-frequency apparatus comprising a first section of rectangular wave guide, a second section of rectangular wave guide having its longitudinal axis parallel to the longitudinal axis of the first wave guide section, the second section having a narrow wall in common with a broad wall of the first section, means in the common wall for directionally coupling the first and second wave guide sections, a third rectangular wave guide section having its longitudinal axis parallel to the longitudinal axis of the first wave guide section, the third section having a broad wall in common with a narrow wall of the first section, means in the common wall for directionally coupling the first and third wave guide sections, a section of circular wave guide having its longitudinal axis extending parallel to the longitudinal axes of the rectangular wave guide sections, the circular wave guide section being' posit'io ned with the wall thereof joined in tangential relationship to a broad wall of the second wave guide section and a narrow wall of the third wave guide section, directional coupling means coupling the circular wave "guide section respectively tothe, second and third wave guide sections, thetrespective directional coupling means extending between the circular wave guide and the second and third waveguide sections in the regions where the respective walls are joined and being displaced in a direction parallel to said longitudinal axes from the respective means coupling said first wave guide section to said second and thirdwave guide sections, the second and third wave guide sections each being. terminated in a short circuit at the end thereof nearer the directional coupling means which couples said second and third wave guide sections with the first wave guide section, the physical path lengths between the first rectangular wave guide section and the circular waveguide section via the second and third wave guide sections being equal, means for terminating the other ends of the second and third wave guide sections in a non-reflective termination, a first ninety-degree phase shifter positioned in the second wave guide between the short-circuited end thereof and the directional coupling means which couplesthe second wave guide section with the first-waveguide section, and a second ninety-degree phase shifter positioned in the second wave guide between the directional-coupling means which couples the second waveguide section with the first wave guide section and the directional coupling means which couples the second waveguide section with the circular wave guide section.

2. Ultra highrfrequency apparatus comprising a first section of rectangular wave guide, a second section of rectangular wave guide having its longitudinal axis parallel to the longitudinal axis of the first'wave guide section, the

"second section'having a wall in common with a wall of the first section, means in the common wall for directionally coupling the first and second wave guide sections, a third rectangular wave guidesection having its longitudinal axis par'all'elto the" longitudinal axis of the first wave guide section, the third section having a wall in common' with a wall of; the first section, means in the common wall for directionally coupling the first'and third wave guide sections, a section of circular wave guide having its longitudinal axis extendingp aralleltothe longitudinal axes of the rectangular wave guide sections, the circular wave guide section being positioned with the wall thereof joined in tangential relationshipto a wall of the second wave guide section and a wall of the third wave guide section,

directional coupling means coupling the circular wave guide section respectively to the second and third wave guide sections, the respective directional coupling means extending between the circular wave guide and the second and third wave' guide sections in the regions where the respective walls are joined and being displaced in a'direction parallel to said longitudinal axes from the respective meanscouplingsaid first waveguide section to said second and third wave guide sections, the second and third wave guide sections each being'terrninateddn a short circuit at the end thereof nearer the-directional coupling means which couples said second and third wave guide sections with the first wave guide section, the physical path lengths between the first rectangular wave guide section and the circular wave guide section via the second and third wave guide sections being equal, means for terminating the other ends of the second and third wave guide sections in a non-reflective termination, a first ninety-degree phase shifter positioned in the second wave guide between the short-circuited end thereof and the directional coupling means whichcouples the second wave guide section with the first wave guide section, and a second ninety-degree phase shifter positioned in the second wave guide between the directional coupling means which couples the second wave guide section with the first wave guide section and the directional coupling means which couples the second wave guide section with the circular wave guide section.

3. Ultra-high-frequency apparatus comprising a first section of rectangular wave guide, a second section of rectangular wave guide, the second section having a wall in common with a wall of the first section, means in'the common wall for directionally coupling the first and second wave guide sections, a third rectangular wave guide section, the third section having a wall in common with a wall of the first section, means in the common wall for directionally coupling the first and third wave guide sections, a section of circular wave guide being positioned with the wall thereof joined in tangential relationship to a wall of the second wave guide section and a wall of the third wave guide section, directional coupling means coupling the circular wave guide section respectively to the second and third wave guide sections, the directional coupling means extending between the circular and second wave guide sections in the region where their respective walls are joined, and being displaced along the second wave guide section from the means coupling said second and first wave guide sections, the directional coupling means extending between the circular and third wave guide sections in the region where their respective walls are joined, and being displaced along the third wave guide section from the means coupling said third and first wave guide sections, the second and third wave guide sections each being terminated in a short circuit at the end thereof nearer the directional coupling means which couples said second and third wave guide sections with the first wave guide section, the physical path lengths between the first rectangular wave guide section and the circular wave guide section via the second and third wave guide sections being equal, means for terminating the other ends of the second and third wave guide sections in a non-reflective termination, a first ninety-degree phase shifter positioned in the second wave guide between the short-circuited end thereof and the directional coupling means which couples the second wave guide section with the first wave guide section, and a second ninety-degree phase shifter positioned in the second wave guide between the directional coupling means which couples the second wave guide section with the first wave guide section and the directional coupling means which couples the second wave guide section with the circular wave guide section.

4. Ultra-high-frequency apparatus comprising a first section of rectangular wave guide, a second section of rectangular wave guide, means for directionally coupling the first and second wave guide sections, a third rectangular wave guide section, means for directionally cou pling the first and third wave guide sections, a section of circular wave guide being positioned with the wall thereof joined in tangential relationship to a wall of the second wave guide section and a wall of the third wave guide section, directional coupling means coupling the circular wave guide section respectively to the second and third wave guide sections, the directional coupling means extending between the circular and second 'wave guide sections in the region where their respective walls are oined,

and being displaced along the second wave guide section from the means coupling said second and first wave guide sections, the directional coupling means extending between the circular and third wave guide sections in the region where their respective walls are joined, and being displaced along the third wave guide section from the means coupling said third and first wave guide sections, the

second and third Wave guide sections each being terminated in a short circuit at the end thereof nearer the directional coupling means which couples said second and third wave guide sections with the first wave guide section, the

physical path lengths between the first rectangular wave guide section and the circular wave guide section via the second and third wave guide sections being equal, a first ninety-degree phase shifter positioned in the second wave guide between the short-circuited end thereof and the directional coupling means which couples the second wave guide section with the first wave guide section, and a second ninety-degree phase shifter positioned in the second wave guide between the directional coupling means which couples the second wave guide section with the first wave guide section and the directional coupling means which couples the second wave guide section with the circular wave guide section.

5. Ultra-high-frequency apparatus comprising a first section of rectangular wave guide, a second section of rectangular wave guide, means for directionally coupling the first and second wave guide sections, a third rectangular wave guide section, means for directionally coupling the first and third wave guide sections, a section of circular wave guide, directional coupling means coupling the circular wave guide section to the second wave guide section and being displaced along the second wave guide section from the means coupling the first and second wave guide sections, directional coupling means coupling the circular Wave guide section to the third wave guide section and being displaced along the third Wave guide section from the means coupling the first and third Wave guide sections, the second and third wave guide sections each being terminated in a short circuit at the end thereof nearer the directional coupling means which couples said second and third Wave guide sections with the first wave guide section, the physical path lengths between the first rectangular wave guide section and the circular Wave guide section via the second and third wave guide sections being equal, a first ninety-degree phase shifter positioned in the second wave guide between the short-circuited end thereof and the directional coupling means which couples the second wave guide section with the first wave guide section, and a second ninety-degree phase shifter positioned in the second wave guide between the directional coupling means which couples the second wave guide section with the first wave guide section and the directional coupling means which couples the second wave guide section with the circular Wave guide section.

6. Means for coupling energy between a rectangular wave guide and circular wave guide, the energy being propagated in the TElO mode in the rectangular Wave guide and propagated in the circular polarized TE11 mode in the circular wave guide, said means comprising first and second wave guide directional couplers, each coupler including a primary wave guide section comprising a portion of said rectangular wave guide and a secondary wave guide section short circuited at one end, third and fourth wave guide directional couplers, each coupler having a primary wave guide section coupled at one end thereof to the other end of the secondary waveguide section of a respective one of the first and second directional couplers and a secondary circular wave guide section contiguous with said circular wave guide, the third and fourth directional couplers being positioned at radially perpendicular positions relative to the circular wave guide, whereby the respective coupled waves in the circular wave guide are perpendicular to each other, the physical path length between the rectangular wave guide and the circu- 7 larjwave via the first and third couplers-being equal to I the physical 'path' length, via the sect n d" and-fourth couplers, aiidfa 1 pair of ninety-degree "phase shifters positioned at either-"end of the secondary wave guide sectiori of the first directional coupler.

7. Means'for coupling energybetween a. rectangular waveguide and circular wave guide, the energy being propagated in the TEmimode in the rectangular 'wave guide and propagated in the circular polarized TEn mode in the circular waveguide, said means comprising first and second wave guide directional couplers, each coupler including a primary wave guide section comprising a portion of "said rectangular wave guide and a secondary wave guide section short circuited at one end, third and v fourth Wave guide directional couplers, each coupler having a primary wave guide section coupled to the secondary wave guide section ofa respective one of the first and second directional couplers anda secondary circular wave guide Section contiguous with said circular wave guide, thethird and fourth directional couplers being positioned at radiallyperpendicular positions relative to the circular wave guide, whereby the respective coupled waves in the circular wave guide are perpendicular to each other, means for producing a ninety-degree phase shift in energy coupled directly between the first and third directional couplers relative to energy coupled directly between the sec- 0nd and fourth directional couplers, and means for producing a phase reversal of energy reflected by the short circuit at the end of the secondary wave guide section of the first directional coupler relative to energy reflected by the short circuit at the end of the secondary wave guide section of the second directional coupler.

8. Apparatus for producing circular polarized waves in a circular wave guide from energy propagated in a rec- "8 tangulanwave guide-in which the direction of-r'otation of the'circularlypolariied waveis'det'erm'ined by the direction of pro agation in t'he rectangular wave guide, said apparatus comprising means coupled-to the rectangular wave-'guideand responsive to energy propagated in one direction insaid wave-guide for producing first and second signals, means'forcoupling'said first and second signals throughthe-cylindrical walls of said circular wave guide at points on mutually perpendicular radii whereby the coupled waves in the circular wave guide have mutually perpendicular'electric fields, means for-shifting the relative phase ofsaid first and second signals by ninety degrees to bring them into phase quadrature, means coupled to the rectangular wave guide'and responsive to energy propagated in the other direction insaid wave guide for'producing third and fourth signals, means for coupling said thirdand fourth signals through the cylindrical walls of said circular wave guide at points on mutually perpendicular radii, and means for shifting the relativerphase of the second and third signal by ninety degrees but in the opposite sense as theshift in phase between the. first and second signals, whereby the third and fourth signals produced circularly polarized waves of the opposite direction of 'rotation from the circularly polarized waves produced by'the firstand'secon'd signals.

References Cited in the file of this patent UNITED STATES PATENTS 2,568,090 Riblet Sept. 18, 1951 2,723,377 Cohn Nov. s, 1955 FOREIGN PATENTS 592,224 Great'Britain Sept. 11, 1947 

